Field of the Invention
The invention relates to an image sensor and more particularly to an image sensor capable of collecting a pure infrared (IR) signal for 3D detection imaging application, ex. Time-of-flight (ToF) technology.
Description of the Related Art
Currently, time-of-flight (ToF) technology has been used extensively in modern industries to provide three dimensional (3D) imaging by using a complementary metal-oxide semiconductor (CMOS) pixel array together with a modulated light source. 3D TOF cameras are used for many different applications, for example, profile inspection of manufactured goods, computer-aided design (CAD) verification, geographic surveying and object imaging.
A 3D ToF camera works by illuminating the scene with a modulated light source, and observing the reflected light. The phase shift between the illumination and the reflection is measured and translated into distance. Typically, the illumination is from a solid-state laser or a light-emitting diode (LED) operating in the near-infrared range of about 850 nm, invisible to the human eye. An imaging sensor designed to respond to the same spectrum of the modulated light source receives the light and converts the photonic energy to electrical current to obtain distance (depth) information of the scene.
However, the light entering the imaging sensor has an ambient component and a reflected component. The distance (depth) information is only embedded in the reflected component. Thus, the ambient component reduces the signal-to-noise ratio (SNR) of the distance (depth) information.